The long-term goal of our investigations is to understand how neural circuits in the auditory system underlie the processing of sound. Understanding this circuitry is likely to have an impact on the diagnosis and treatment of clinically important central neuropathologies, including autism, schizophrenia, tinnitus, Tourette's syndrome and obsessive compulsive disorder. The central goal of this proposal is to understand how the output of the auditory cortex is used by downstream areas to effect behavior. In Aim 1 we use electrophysiological methods to study responses in the auditory cortex and target areas during a sound categorization task. In Aim 2 we use optogenetic methods to test the hypotheses that the activity of output neurons in the auditory cortex is causal in mediating behavior during the task. Finally in Aim 3, we test the hypothesis that learning to perform an auditory categorization modifies connections between neurons in their auditory cortex and their downstream targets. These studies will provide insight into how auditory cortex guides behavior, and provide a foundation for further study of role of these neurons in normal auditory function and disease, facilitating the development of treatments for psychiatric and neurological diseases.